Continuous heat treatment method and apparatus mainly for reactive metals

ABSTRACT

A method of continuously heat treating reactive metals by passing the reactive metal through an heat treatment apparatus in which an inert gas is maintained at a pressure higher than atmospheric pressure and the interior of which is divided into a material inlet portion, a heat treating portion and a material outlet portion arranged in the order mentioned with a lip seal interposed between each other, the pressure distribution of the inert gas in the apparatus being such that the pressure is progressively reduced from the heat treating portion wherein it is highest, toward the material inlet portion and toward the material outlet portion stepwise; and an apparatus for practicing said method.

United States Patent [191 Tokuda et al.

Filed: Nov. 16, 1970 Appl. No.: 89,566

[73] Assignee:

[30] Foreign Application Priority Data Nov. 15, 1969 Japan 44/91661 U.S.CI. 266/3 R, 148/203, 148/156 Int. Cl. (321d 9/56 Field of Search 266/3R, 5 R;

References Cited UNITED STATES PATENTS- 6/1908 Thompson 266/3 R Aug. 14,1973 890,314 6/1908 Thompson 266/3 R 1,987,577 1/1935 Moers 266/3 RPrimary Examiner-Gerald A. Dost Anomey-Oblon, Fisher & Spivak [57]ABSTRACT A method of continuously heat treating reactive metals bypassing the reactive metal through an heat treatment apparatus in whichan inert gas is maintained at a pressure higher than atmosphericpressure and the interior of which is divided into a material inletportion, a heat treating portion and a material outlet portion arrangedin the order mentioned with a lip seal interposed between each other,the pressure distribution of the inert gas in the apparatus being suchthat the pressure is progressively reduced from the heat treatingportion wherein it is highest, toward the material inlet portion andtoward the material outlet portion stepwise; and an apparatus forpracticing said method.

2 Claims, 8 Drawing Figures rLLII/IIIII I I I F e 1." 7 L K 5 /I .9 9 9/0 9 9 PAIENTED M 14 I75 sum 1 or 2 F/G. lb

& 2G Emi m wmmmm A 7M0 SPHER/C PRESSURE INVENTORS SHOICHI TOKUDA SHTOSHIOHTANI MINORU NISIGAKI @Mjw/h u ATTORNEYS PAIENIEllmum 3.'752f,4

SHEEI 2 0F 2 47'M0SPHER/C fi POSITIVE PRESSURE 4/ PRESSURE \x \PLATE 0/?STRIP W/RE 0/? BAR INVENTORS SHOICHI TOKUDA SHITOSHI OHTANI MINORUNISIGAKI BY @Mm, 314% #4 ATTORNEYS I CQNTINUQUS HEAT TREATMENT METHODAND APPARATUSMAINLY FOR REACTIVE METALS The present invention relates toa method of continuously heat treating reactive metals such as titanium,zirconium and tantalum, and to an apparatus used for practicing themethod.

More specifically, the invention relates to a method 7 by which reactivemetals, such as titanium, zirconium and tantalum, in the shape of astrip, sheet, wire or rod, are continuously subjected to heat treatment,mainly to annealing or solution treatment; and also to a heat treatmentapparatus most suitable for practicing such method.

Heretofore, heat treatment of reactive metals, such as titanium,zirconium, tantalum and alloys thereof, has been carried out batchwisein a furnace which is previously evacuated completely by a vacuum pumpor the interior atmosphere of which is previously substituted by such aninert gas as argon after completely evacuating the furnace by a vacuumpump, so as to prevent oxidation of the metal to the fullest possibleextent. However, in these methods some surface oxidation of the metal isinevitable and it has been customary to remove such an oxide layer,formed on the surface of the metal, either mechanically or chemicallysubsequent to the heat treatment. Furthermore, with such a conventionalfurnace, much difficulty has been encountered in quenching the metalsuccessively to the heat treatment and, even if the quenching of themetal might be achieved in water or other liquid, the metal would besubjected to oxidation during quenching or to a heavy distortion in caseof a sheet metal, which calls for cumbersome procedures in thesubsequent treatment.

Further, it has been an essential problem that the heat treatment ofsuch metals as mentioned above has been effected solely batchwise andcontinuous heat treatment has been impossible though it has been desired in the art.

The present invention has been achieved with a view to providing amethod of and an apparatus for continuously heat treating reactivemetals, such as titanium, zirzonium and tantalum, without causingsurface oxidation of the metals.

The method and apparatus of the instant invention are'applicable to thereactive metals in the shape of a strip, sheet, wire and rod. The heattreatment which the present invention primarily aims to achieve, is thescalled annealing in which a metal is cooled slowly after heating, orthe so-called solution treatment in which a metal is cooled rapidlyafter heating.

According to one aspect of the invention, there is provideda method ofcontinuously heat treating metals in an inert gas atmosphere, whichcomprises heat treatingia metal by passing it through heat treatmentapparatus, in which an inert gas is maintained at a pressure higher thanatmospheric pressure and the interior of which=is divided into a heattreating portion wherein themetal; is heated and cooled, and a materialinlet portion and a material outlet portion which are located on the;opposite-.sides of said heat treating portion, the pressuredistribution of the inert gas in the apparatus beingsuch that thepressure in the heat treating portion is highest andis progressivelyreduced toward the ma terial inlet portion and toward the materialoutlet portion stepwise.

, scribed method, which comprises a material inlet por- According toanother aspect of the invention, there is provided an apparatus forpracticing the abovedevention;

tion, a differential pressure maintaining portion, a heat treatingportion, a differential pressure maintaining portion and a materialoutlet portion, all of which are arranged in series in the ordermentioned and connected with each other integrally with a lip sealinterposed between each other.

An embodiment of the present invention will be described hereinafterwith reference to the accompanying drawings. In the drawings,

FIG. 1(A) is a diagrammatical view showing an embodiment of theapparatus according to the present in- FIG. 1(B) is a diagram showingthe pressure distribution in the apparatus of FIG. 1(A); and

FIGS. 2 through 5 are diagrammatical views exemplifying variousconstructions of the cooling chamber of the apparatus respectively.

FIGS. 6 and 7 are detailed construction of the lip seals 8 suitable forplate and rod, respectively.

Referring to FIG. 1(A), reference numeral 1 designates an entrance ofthe apparatus, 2 a material inlet portion, 3 a differential pressuremaintaining portion, 4a a heating chamber, 4b a cooling chamber, (theheating chamber 4a and the cooling chamber 4b together composing a heattreating portion 4), 5 a differential pressure maintaining portion, 6 amaterial outlet portion and 7 an exit of the apparatus. Lip seals 8 areprovided each at the entrance 1, between the material inlet portion 2and the differential pressure maintaining portion 3, between thedifferential pressure maintaining portion 3 and the heat treatingportion 4, between the heat treating portion 4 and the differentialpressure maintaining portion 5, between the differential pressuremaintaining portion 5 and the material outlet portion 6, and at the exit7 of the apparatus, and the respective portions are connected with eachother integrally through these lip seals 8. The heat treating portion 4,the differential pressure maintaining portions 3 and 5, the materialinlet portion 2 and the material outlet portion 6 are each provided withan inert gas inlet port 9.

Since the lip seals 8 are provided at the opposite ends of each portion,when an inert gas is introduced into the respective portions through theinert gas inlet ports .9, upon evacuating the interior of the apparatusby any means, to a pressure higher than the atmospheric pressure in sucha manner that the flow rate of the inert gas is highest for the heattreating portion 4 and is progressively decreased for the differentialpressure maintaining portions 3 and 5, the material inlet portion 2 andthe material outlet portion 6 in the order mentioned, a pressuredistribution as shown in FIG. 1(B) is obtained in the apparatus. Namely,the inert gas pressure is highest in the heat treating portion and isprogressively reduced stepwise in the respective portions toward theopposite ends of the apparatus. When a material to be treated issuccessively passed through the lip seals 8, each of said lip seals actsas a type of orifice and the inert gas flows from the higher pressureside to the lower pressure side. However, the pressure distributionshown in FIG. 1(B) can be maintained by replenishing the inert gas intothe respective portions through the inert gas inlet ports 9. In thiscase, since the pressure in the differential pressure maintainingportions 3 and 5 is made only slightly lower than that in the heattreating portion 4, an abrupt pressure drop in said heat treatingportion due to release of the gas therefrom can be prevented. Further,since the pressure in the differential pressure maintaining portions 3and is higher than that in the material inlet portion 2 and the materialoutlet portion 6, the intrusion of air into the heat treating-portion 4can be prevented by said differential pressure maintaining portion 3 or5 even if air flows into the material inlet portion 2' or the materialoutlet portion 6 due to failure of the lip seal 8 at the entrance 1 orthe exit 7 of the apparatus, upon occurrence of such failure for somereasons during continuous heat treatment of an elongate material.

If the heat treatment is conducted in the inert gas of such pressuredistribution, there will be no fear of air intruding into the apparatusfrom the outside even when the heat treatment is carried outcontinuously.

The construction of the cooling chamber 4b is variable widely, dependingupon the configuration of the material to be treated and the conditionsunder which the heat treatment is effected. Different constructions ofthe cooling chamber 412 are exemplified in FIGS 2 through 5. FIG. 2shows a type of cooling chamber which is adapted for use in the heattreatment of a sheet material and is composed of a pair of copper plates1 1 each having a cooling jacket therein for the circulation of acooling medium 10 and arranged in opposed relation to each other forcooling a material 12, passing therebetween, by absorbing the radiantheat of said material. The cooling device shown in FIG. 2 can be usedfor cooling a rod shaped material, by replacing the copper plates 11with a coiled spiral copper tube. FIG. 3 shows another type of coolingchamber in which one or a plurality of copper pinch rolls 13, eachhaving a cooling jacket, are provided and a sheet or rod material 12 iscooled rapidly by passing it through said pinch rolls. FIG. 4 showsstill another type of cooling chamber in which a material is cooled bythe blasts of an inert gas 14 ejected from the opposed copper plates 11of the type shown in FIG. 2. Further, where a material to be treated hasa limited length, the arrangement shown in FIG. 5 may be used, in whichopposed copper plates 14 of the type shown in FIG. 2 are pressed againsta sheet material 12 to be treated from both sides by hydraulic means orother means 15 to rapidly cool said material.

In the embodiment described and illustrated herein, the pressure in theapparatus is elevated in two steps from the entrance 1 to the heattreating portion 4 and is lowered also in two steps from the heattreating portion 4 to the exit 7, by interposing the material inletportion 2 and the differnetial pressure maintaining portion 3 betweensaid entrance and said heat treating portion, and the differentialpressure maintaining portion 5 and the material outlet portion 6 betweensaid heat treating portion and said exit. However, the pressure may bevaried in one step, provided that the sealing between the adjacentportions is effected more completely. In other words, the object of theinvention may be attained by using the material inlet portion 2 and thematerial outlet portion 6 simultaneously as the differential pressuremaintaining portions 3 and 5 respectively and thereby eliminating saiddifferential pressure maintaining portions.

For moving the material to be treated through the apparatus, a materialsuspending conveyor may be used or coiling devices may be provided atboth the entrance and exit of the apparatus. It will, therefore, be seenthat the apparatus of the invention may be used in both a verticalposition or a horizontal position.

Now, the method of the present invention will be further described byway of example.

EXAMPLE Ti-l4Mo-5Zr alloy sheets were subjected to annealing in theapparatus shown in FIG. 1 in which the differential pressure maintainingportions 3 and 5 were eliminated and the cooling chamber was constructedas shown in FIG. 2 under such conditions that the temperature of theheating portion was 900C., the flow rate of argon gas was 6 /min and theannealing rates were 400 mm/min (in the case of a sheet having athickness of 0.15 mm) and 200 mm/min (in the case of a sheet having athickness of 0.85 mm). The alloy sheets thus annealed had no colorindicative of oxidation and glossy sheets were obtained. Further, theannealed alloy sheets had the mechanical properties as shown in Table 1below, indicating that they had been sufficiently annealed.

TABLE 1 Mechanical Properties of Annealed Ti-l5Mo-5Zr Alloy Sheets Sam-Thick- Rate of Tensile E-lonErich- Hardple ness Annealing Strength gasenness No. (mm) (mm/min) (kg/mm) tion (mm) (Hv) Although in the Examplegiven above, titanium alloy only was used, it is to be understood thatthe present invention is highly effectively used in the heat treatmentof not only reactive meals, such as titanium, but also those metals,such as special steels and nickelbased alloys, which require a specialheat treatment.

Further, although argon gas was used in the Example as an inert gas, anyother gases may be used which will not provide an oxidizing atmospherein the heat treatment apparatus.

According to the present invention, as described above, a pressuredistribution as shown in FIG. 1(B) can be obtained only by providing thelip seals which are very simple in structure. Therefore, an elongatematerial can be heat treated continuously in a nonoxidized state, whilemaintaining the inert gas atmosphere in the apparatus. Further, sincethe heat treatment can be carried out continuously, uniform heating andcooling are possible and hence a heat treated material of high qualitycan be 0obtained. It is the particularly remarkable advantage of theinvention that by practicing the invention, oxidation-free, glossyannealing of a thin sheet material or foil becomes possible which hasbeen considered extremely difficult. The present invention is alsoadvantageous in that rapid cooling and slow cooling can be achieved inthe same apparatus. Namely, when the cooling chamber of the constructionshown in FIG. 2 is used, the cooling rate can be controlled by changingthe travelling speed of the material to be treated, whereas when thecooling chamber of the construction shown in FIG. 3 or 4 is used, thematerial can be cooled rapidly. There is a further advantage that aheavy distortion of the material, which has been encounteredparticularly in rapid cooling of a sheet material, can be substantiallyeliminated by pressing the cooling plates, such as copper plates,

against the material from both sides.

We claim:

ll. An apparatus for continuously heat treating metals, comprising amaterial inlet portion, a differential pressure maintaining portion, aheat treating portion, a differential pressure maintaining portion, amaterial outlet portion,all of which are arranged in series in the ordermentioned and connected with each other integrally with a lip sealinterposed between each other, and means for pressurizing all of saidportions with gas such that the pressure within each portion is aboveatmospheric and increases in a discontinuous,step-wise fashion whenproceeding from said inlet portion toward said heat treating portion anddecreases in a discontinuous, step-wise fashion when proceeding fromsaid heat treating portion to said outlet portion.

2. An apparatus for continuously heat treating metals, comprising amaterial inlet portion serving the function of maintaining adifferential pressure, a heat treating portion, a material outletportion serving the function of maintaining a differential pressure,allof which are'arranged in series in the order mentioned and connectedwith each other integrally with a lip seal interposed between each otherand means for pressurizing all of said portions with gas such that thepressure within each portion is above atmospheric and increases in adiscontinuous, step-wise fashion when proceeding from said inlet portionto said heat treating portion and decreases in a discontinuous,step-wise fashion when proceeding from said heat treating portion tosaid outlet portion.

2. An appaRatus for continuously heat treating metals, comprising amaterial inlet portion serving the function of maintaining adifferential pressure, a heat treating portion, a material outletportion serving the function of maintaining a differential pressure,allof which are arranged in series in the order mentioned and connectedwith each other integrally with a lip seal interposed between each otherand means for pressurizing all of said portions with gas such that thepressure within each portion is above atmospheric and increases in adiscontinuous, step-wise fashion when proceeding from said inlet portionto said heat treating portion and decreases in a discontinuous,step-wise fashion when proceeding from said heat treating portion tosaid outlet portion.